Heat exchanger and method of manufacturing outside plate used for header tanks of heat exchanger

ABSTRACT

A method of manufacturing an outside plate used for a heat exchanger header tank configured such that an outside plate having an outwardly bulging portion, an inside plate, and an intermediate plate are brazed together in layers. A thick portion is formed on an outside-plate forming metal plate at a center portion with respect to the width direction thereof. Subsequently, a press work is performed on the outside-plate forming metal plate so as to form the outwardly bulging portion by making use of the thick portion. A connection portion having a curvature radius of 1 mm or less is formed between an inner wall surface of the outwardly bulging portion and each of surfaces of the outside plate located on the opposite sides of the outwardly bulging portion. This method enables manufacture of an outside plate which reduces the weight while securing sufficient withstanding pressure.

BACKGROUND OF THE INVENTION

The present invention relates to a heat exchanger and a method of manufacturing an outside plate used for header tanks of a heat exchanger. More particularly, the present invention relates to a heat exchanger that can be favorably used as a gas cooler or an evaporator of a supercritical refrigeration cycle in which a CO₂ (carbon dioxide) refrigerant or a like supercritical refrigerant is used, and to a method of manufacturing an outside plate used for header tanks of such a heat exchanger.

Herein and in the appended claims, the term “supercritical refrigeration cycle” means a refrigeration cycle in which a refrigerant on the high-pressure side is in a supercritical state; i.e., assumes a pressure in excess of a critical pressure. The term “supercritical refrigerant” means a refrigerant used in a supercritical refrigeration cycle. Also, herein and in the appended claims, the downstream side of flow (represented by arrow X in FIG. 1) of air through air-passing clearances between adjacent heat exchange tubes will be referred to as the “front,” and the opposite side as the “rear.”

A conventionally known heat exchanger for use in a supercritical refrigeration cycle includes a pair of header tanks disposed apart from each other; flat heat exchange tubes disposed in parallel at intervals between the two header tanks and having opposite end portions connected to the respective header tanks; and fins disposed in respective air-passing clearances between the adjacent heat exchange tubes and brazed to the heat exchange tubes (refer to Japanese Patent Application Laid-Open (kokai) No. 2005-300135). Each of the two header tanks is configured such that an outside plate, an inside plate, and an intermediate plate intervening between the outer and inside plates are brazed together in layers. The outside plate has an outwardly bulging portion extending in the longitudinal direction thereof and having an opening closed by the intermediate plate. The inside plate has a plurality of tube insertion holes in the form of through-holes formed in a region corresponding to the outwardly bulging portion of the outside plate and spaced apart from one another along the longitudinal direction thereof. The intermediate plate has a plurality of communication holes slightly larger than the tube insertion holes of the inside plate and in the form of through-holes formed for allowing the respective tube insertion holes to communicate with the interior of the outwardly bulging portion of the outside plate. Opposite end portions of the heat exchange tubes are inserted through the respective tube insertion holes of the inside plates and into the respective communication holes of the intermediate plates of the two header tanks. The entire outer peripheral surfaces of opposite end portions of the heat exchange tubes are brazed to the respective entire peripheral wall surfaces of the tube insertion holes of the inside plates of the two header tanks. At least one outwardly bulging portion of each header tank serves as a refrigerant-flow outwardly bulging portion in which refrigerant flows in the longitudinal direction thereof. In each header tank, the communication holes of the intermediate plate communicating with the refrigerant-flow outwardly bulging portion are connected together by means of communication portions formed in the intermediate plate.

In the heat exchanger described in the publication, in order to increase the withstanding pressure of each header tank, the outside plate is formed of an aluminum plate having a relatively large thickness and through a press work performed thereon. However, in this case, the weight of the heat exchanger increases.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above problem and to provide a heat exchanger which has a reduced weight and whose header tanks have a sufficient withstanding pressure, and a method of manufacturing an outside plate used for header tanks of a heat exchanger.

To fulfill the above object, the present invention comprises the following modes.

1) A heat exchanger comprising a pair of header tanks disposed apart from each other and a plurality of flat heat exchange tubes disposed in parallel between the two header tanks and having opposite end portions connected to the respective header tanks, each of the two header tanks being configured such that an outside plate, an inside plate, and an intermediate plate intervening between the outside and inside plates are brazed together in layers, the outside plate having an outwardly bulging portion extending in a longitudinal direction thereof and having an opening closed by the intermediate plate, the inside plate having a plurality of tube insertion holes in the form of through-holes formed in a region corresponding to the outwardly bulging portion of the outside plate and spaced apart from one another along a longitudinal direction of the inside plate, and the intermediate plate having a plurality of communication holes in the form of through-holes formed for allowing the respective tube insertion holes of the inside plate to communicate with the interior of the outwardly bulging portion of the outside plate,

wherein the outside plate of each header tank is formed of a metal plate and through a press work performed thereon, and a connection portion between an inner wall surface of the outwardly bulging portion of the outside plate and a surface of the outside plate which surface is joined to the intermediate plate has a curvature radius of 1 mm or less.

2) A heat exchanger according to par. 1), wherein the connection portion between the inner wall surface of the outwardly bulging portion and the surface of the outside plate joined to the intermediate plate has a curvature radius of 0.5 mm or less.

3) A heat exchanger according to par. 1), wherein the outside plate has a thickness of 2 mm or greater.

4) A method of manufacturing an outside plate used for a heat exchanger header tank which is configured such that an outside plate, an inside plate, and an intermediate plate intervening between the outside and inside plates are brazed together in layers, the outside plate having an outwardly bulging portion extending in a longitudinal direction thereof and having an opening closed by the intermediate plate, the inside plate having a plurality of tube insertion holes in the form of through-holes formed in a region corresponding to the outwardly bulging portion of the outside plate and spaced apart from one another along a longitudinal direction of the inside plate, and the intermediate plate having a plurality of communication holes in the form of through-holes formed for allowing the respective tube insertion holes of the inside plate to communicate with the interior of the outwardly bulging portion of the outside plate, the method comprising the steps of:

forming a thick portion on an outside-plate forming metal plate at a center portion with respect to the width direction thereof, the thick portion being thicker than the remaining thin portion; and

performing a press work on the outside-plate forming metal plate so as to form the outwardly bulging portion by making use of the thick portion such that a connection portion having a curvature radius of 1 mm or less is formed between an inner wall surface of the outwardly bulging portion and each of surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface.

5) A method of manufacturing an outside plate used for a heat exchanger header tank according to par. 4), wherein the thick portion is formed by performing a press work on the outside-plate forming metal plate.

6) A method of manufacturing an outside plate used for a heat exchanger header tank according to par. 5), wherein the thick portion of the outside-plate forming metal plate has a thickness 1.05 to 1.5 times that of the remaining thin portion.

7) A method of manufacturing an outside plate used for a heat exchanger header tank according to par. 4), wherein a connection portion having a curvature radius of 0.5 mm or less is formed between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface.

8) A method of manufacturing an outside plate used for a heat exchanger header tank according to par. 4), wherein the outside plate has a thickness of 2 mm or greater in its final shape.

9) A method of manufacturing an outside plate used for a heat exchanger header tank which is configured such that an outside plate, an inside plate, and an intermediate plate intervening between the outside and inside plates are brazed together in layers, the outside plate having an outwardly bulging portion extending in a longitudinal direction thereof and having an opening closed by the intermediate plate, the inside plate having a plurality of tube insertion holes in the form of through-holes formed in a region corresponding to the outwardly bulging portion of the outside plate and spaced apart from one another along a longitudinal direction of the inside plate, and the intermediate plate having a plurality of communication holes in the form of through-holes formed for allowing the respective tube insertion holes of the inside plate to communicate with the interior of the outwardly bulging portion of the outside plate, the method comprising the steps of:

performing a first press work on an outside-plate forming metal plate so as to form a preliminary bulging portion having a bulging height greater than that of the outwardly bulging portion; and

performing a second press work on the outside-plate forming metal plate having the preliminary bulging portion, while restraining the outside-plate forming metal plate from the opposite sides with respect to the width direction thereof, so as to form the outwardly bulging portion from the preliminary bulging portion such that a connection portion having a curvature radius of 1 mm or less is formed between an inner wall surface of the outwardly bulging portion and each of surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface.

10) A method of manufacturing an outside plate used for a heat exchanger header tank according to par. 9), wherein the step of performing the second press work includes cutting opposite side edge portions of the outside-plate forming metal plate by use of one of dies used for the press work before formation of the outwardly bulging portion from the preliminary bulging portion, and restraining the outside-plate forming metal plate having the preliminary bulging portion from the opposite sides with respect to the width direction thereof by use of the die.

11) A method of manufacturing an outside plate used for a heat exchanger header tank according to par. 9), wherein a connection portion having a curvature radius of 0.5 mm or less is formed between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface.

12) A method of manufacturing an outside plate used for a heat exchanger header tank according to par. 9), wherein the outside plate has a thickness of 2 mm or greater in its final shape.

According to the heat exchanger of par. 1), the outside plate of each header tank is formed of a metal plate and through a press work performed thereon, and a connection portion between an inner wall surface of the outwardly bulging portion and a surface of the outside plate which surface is joined to the intermediate plate has a curvature radius of 1 mm or less. Therefore, the stress concentration at the connection portion between the inner wall surface of the outwardly bulging portion and the surface of the outside plate joined to the intermediate plate is mitigated, and thus, the withstanding pressure of the header tank increases. In addition, since the withstanding pressure is increased through mitigation of the stress concentration at the connection portion between the inner wall surface of the outwardly bulging portion and the surface of the outside plate joined to the intermediate plate, the thickness of the outside plate can be reduced as compared with the heat exchanger disclosed in the above-described publication. Accordingly, the weight of the header tanks, and thus, the weight of the entire heat exchanger using the header tanks can be reduced.

According to the heat exchanger of par. 2), the connection portion between the inner wall surface of the outwardly bulging portion and the surface of the outside plate joined to the intermediate plate has a curvature radius of 0.5 mm or less. Therefore, the stress concentration at the connection portion between the inner wall surface of the outwardly bulging portion and the surface of the outside plate joined to the intermediate plate is mitigated more effectively, and thus, the withstanding pressure of the header tanks increases more.

According to the heat exchanger of par. 3), since the outside plate has a thickness of 2 mm or greater, the withstanding pressure of the header tanks increases.

According to the method of manufacturing an outside plate of par. 4), a thick portion is formed on an outside-plate forming metal plate at a center portion with respect to the width direction thereof, the thick portion being thicker than the remaining thin portion, and a press work is then performed on the outside-plate forming metal plate so as to form the outwardly bulging portion by making use of the thick portion. Therefore, the material of the thick portion flows throughout press working dies, whereby a connection portion having a curvature radius of 1 mm or less can be formed between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface. Accordingly, a heat exchanger header tank using the outside plate manufactured by this method has an increased withstanding pressure. As a result, the thickness of the outside plate can be reduced as compared with the heat exchanger disclosed in the above-described publication, and the weight of the header tanks, and thus, the weight of the entire heat exchanger using the header tanks can be reduced.

In addition, the method of par. 4) enables use of a high-strength aluminum material on which extrusion cannot be performed. This also increases the withstanding pressure of the heat exchanger header tank using the manufactured outside plate.

According to the method of manufacturing an outside plate of par. 5), the thick portion can be formed on the outside-plate forming metal plate relatively easily.

According to the method of manufacturing an outside plate of par. 6), the thick portion of the outside-plate forming metal plate has a thickness 1.05 to 1.5 times that of the remaining thin portion. Therefore, flow of the material of the thick portion throughout the press working dies occurs without fail, so that the outside-plate forming metal plate can be formed into a target shape, and thus, a connection portion having a curvature radius of 1 mm or less can be formed between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface.

According to the method of manufacturing an outside plate of par. 7), a connection portion having a curvature radius of 0.5 mm or less is formed between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface. In a heat exchanger header tank using the outside plate manufactured by this method, the stress concentration at the connection portion between the inner wall surface of the outwardly bulging portion and the surface of the outside plate joined to the intermediate plate can be mitigated more effectively, and thus, the withstanding pressure of the header tank increases more.

In the case where the outside plate to be manufactured has a thickness of 2 mm or greater in its final shape as in the method of manufacturing an outside plate of par. 8), forming into the target shape through a press work is difficult, and when a press work is performed on an outside-plate forming plate without formation of the above-described thick portion, a connection portion having a large curvature radius of, for example, 3 mm or greater may be formed between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface. In a heat exchanger header tank using such an outside plate, stress concentrates at the brazed portions between the intermediate plate and portions of the outside plate located on the front and rear sides of the outwardly bulging portion, whereby the withstanding pressure of the heat exchanger header tank may decrease.

However, even in such a case, according to the method of par. 4), the curvature radius of the connection portion between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface can be made 1 mm or less. Accordingly, the stress concentration at the brazed portions between the intermediate plate and portions of the outside plate located on the front and rear sides of the outwardly bulging portion can be mitigated.

According to the method of manufacturing an outside plate of par. 9), a first press work is performed on an outside-plate forming metal plate so as to form a preliminary bulging portion having a bulging height greater than that of the outwardly bulging portion, and then a second press work is performed on the outside-plate forming metal plate having the preliminary bulging portion, while restraining the outside-plate forming metal plate from the opposite sides with respect to the width direction thereof. Therefore, the outwardly bulging portion can be formed from the preliminary bulging portion, and the curvature radius of the connection portion between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface can be made 1 mm or less. Accordingly, a heat exchanger header tank using the outside plate manufactured by this method has an increased withstanding pressure. As a result, the thickness of the outside plate can be reduced as compared with the heat exchanger disclosed in the above-described publication, and the weight of the header tanks, and thus, the weight of the entire heat exchanger using the header tanks can be reduced.

In addition, the method of par. 9) enables use of a high-strength aluminum material on which extrusion cannot be performed. This also increases the withstanding pressure of the header tank using the manufactured outside plate.

According to the method of manufacturing an outside plate of par. 10), when the second press work is performed, opposite side edge portions of the outside-plate forming metal plate are cut by use of one of dies used for the press work before formation of the outwardly bulging portion from the preliminary bulging portion, and the outside-plate forming metal plate having the preliminary bulging portion is restrained from the opposite sides with respect to the width direction thereof by use of the die. Therefore, the outside-plate forming metal plate can be restrained from the opposite sides without fail.

According to the method of manufacturing an outside plate of par. 11), a connection portion having a curvature radius of 0.5 mm or less is formed between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface. In a heat exchanger header tank using the outside plate manufactured by this method, the stress concentration at the connection portion between the inner wall surface of the outwardly bulging portion and the surface of the outside plate joined to the intermediate plate can be mitigated more effectively, and thus, the withstanding pressure of the header tank increases more.

In the case where the outside plate to be manufactured has a thickness of 2 mm or greater in its final shape as in the method of manufacturing an outside plate of par. 12), forming into the target shape through a press work is difficult, and when a press work is performed on an outside-plate forming plate without formation of the above-described preliminary bulging portion, a connection portion having a large curvature radius of, for example, 3 mm or greater may be formed between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface. In a heat exchanger header tank using such an outside plate, stress concentrates at the brazed portions between the intermediate plate and portions of the outside plate located on the front and rear sides of the outwardly bulging portion, whereby the withstanding pressure of the heat exchanger header tank may decrease.

However, even in such a case, according to the method of par. 9), the curvature radius of the connection portion between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface can be made 1 mm or less. Accordingly, the stress concentration at the brazed portions between the intermediate plate and portions of the outside plate located on the front and rear sides of the outwardly bulging portion can be mitigated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the overall construction of a gas cooler to which the heat exchanger according to the present invention is applied;

FIG. 2 is a fragmentary view in vertical section showing the gas cooler of FIG. 1 as it is seen frontward from rear;

FIG. 3 is an exploded perspective view showing a first header tank of the gas cooler of FIG. 1;

FIG. 4 is an enlarged view in section taken along line A-A of FIG. 2;

FIG. 5 is an enlarged view in section taken along line B-B of FIG. 2;

FIG. 6 is an enlarged view in section taken along line C-C of FIG. 2;

FIG. 7 is a set of views showing a method of manufacturing the outside plate of the first header tank of the gas cooler of FIG. 1;

FIG. 8 is an exploded perspective view showing a method of manufacturing the first header tank of the gas cooler of FIG. 1;

FIG. 9 is an exploded perspective view showing a method of manufacturing a second header tank of the gas cooler of FIG. 1;

FIG. 10 is a cross-sectional view showing a heat exchange tube of the gas cooler of FIG. 1;

FIG. 11 is a fragmentary enlarged view of FIG. 10;

FIG. 12 is a set of views showing a method of manufacturing the heat exchange tube shown in FIG. 10; and

FIG. 13 is a set of views showing another method of manufacturing the outside plate of the first header tank of the gas cooler of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will next be described in detail with reference to the drawings. These embodiments are implemented by applying a heat exchanger according to the present invention to a gas cooler of a supercritical refrigeration cycle.

In the following description, the upper, lower, left-hand, and right-hand sides of FIGS. 1 and 2 will be referred to as “upper,” “lower,” “left,” and “right,” respectively. Further, in the following description, the term “aluminum” encompasses aluminum alloys in addition to pure aluminum.

FIGS. 1 and 2 show the overall construction of a gas cooler to which the heat exchanger according to the present invention is applied. FIGS. 3 to 6 show the configuration of essential portions of the gas cooler of FIG. 1. FIGS. 7 to 9 show a method of manufacturing header tanks. FIGS. 10 and 11 show a heat exchange tube. FIG. 12 shows a method of manufacturing the heat exchange tube.

With reference to FIG. 1, a gas cooler 1 of a supercritical refrigeration cycle wherein a supercritical refrigerant, such as CO₂, is used includes two header tanks 2 and 3 extending vertically and spaced apart from each other in the left-right direction; a plurality of flat heat exchange tubes 4 arranged in parallel between the two header tanks 2 and 3 and spaced apart from one another in the vertical direction; corrugated fins 5 arranged in respective air-passing clearances between adjacent heat exchange tubes 4 and at the outside of the upper-end and lower-end heat exchange tubes 4 and each brazed to the adjacent heat exchange tubes 4 or to the upper-end or lower-end heat exchange tube 4; and side plates 6 of aluminum arranged externally of and brazed to the respective upper-end and lower-end corrugated fins 5. In the case of this embodiment, the header tank 2 at the right will be referred to as the “first header tank,” and the header tank 3 at the left as the “second header tank.”

As shown in FIGS. 2 to 6, the first header tank 2 is configured such that an outside plate 7, an inside plate 8, and an intermediate plate 9 intervening between the outside plate 7 and the inside plate 8 are brazed together in layers. The outside plate 7 and the inside plate 8 are each formed from a brazing sheet having a brazing material layer on each of opposite sides; herein, an aluminum brazing sheet. The intermediate plate 9 is formed from a bare metal material; herein, a bare aluminum material.

The outside plate 7 has a plurality of; herein, two, dome-like outwardly bulging portions 11A and 11B spaced apart from each other in the vertical direction. The outwardly bulging portions 11A and 11B extend vertically, and have the same bulging height, length, and width. In the outside plate 7, a peripheral portion around a leftward-facing opening of each of the outwardly bulging portions 11A and 11B is brazed to the intermediate plate 9, whereby the intermediate plate 9 covers the leftward-facing openings of the outwardly bulging portions 11A and 11B. As a result, the interior of each of the outwardly bulging portions 11A and 11B serves as a refrigerant flow section whose upper and lower ends are closed. Those portions of the first header tank 2 which correspond to the outwardly bulging portions 11A and 11B serve as respective header sections. The curvature radius R of a connection portion 26 between the inner wall surface of each outwardly bulging portion 11A, 11B and each of inside surfaces of the outside plate 7 which are located on the front and rear sides of the outwardly bulging portion 11A, 11B and which extend in the left-right direction is not greater than 1 mm, preferably, not greater than 0.5 mm (see FIG. 4 and FIG. 6). The outside plate 7 has a thickness of 2 mm or greater.

A refrigerant inlet 12 is formed in a crest portion of the upper outwardly bulging portion 11A of the outside plate 7. An inlet member 13 of a metal; herein, a bare aluminum material, having a refrigerant inflow channel 14 in communication with the refrigerant inlet 12 is brazed to the outer surface of the outwardly bulging portion 11A by use of the brazing material on the outer surface of the outside plate 7. A refrigerant outlet 15 is formed in a crest portion of the lower outwardly bulging portion 11B. An outlet member 16 of a metal; herein, a bare aluminum material, having a refrigerant outflow channel 17 in communication with the refrigerant outlet 15 is brazed to the outer surface of the outwardly bulging portion 11B by use of the brazing material on the outer surface of the outside plate 7. The outside plate 7 is formed, by press work, from an aluminum brazing sheet having a brazing material layer on each of opposite sides.

A plurality of tube insertion holes 18 elongated in the front-rear direction are formed through the inside plate 8 and are vertically spaced apart from one another. An upper-half group of tube insertion holes 18 are formed within a vertical range corresponding to the upper outwardly bulging portion 11A of the outside plate 7. Similarly, a lower-half group of tube insertion holes 18 are formed within a vertical range corresponding to the lower outwardly bulging portion 11B. The tube insertion holes 18 have a front-to-rear length slightly longer than the front-to-rear width of the outwardly bulging portions 11A and 11B such that front and rear end portions of the tube insertion holes 18 project outward beyond the front and rear ends, respectively, of the outwardly bulging portions 11A and 11B. Front and rear edge portions of the inside plate 8 have integrally formed respective cover walls 19. The cover walls 19 project rightward such that their ends reach the outer surface of the outside plate 7, and cover respective boundary portions between the outside plate 7 and the intermediate plate 9 along the overall length of the boundary portions. The cover walls 19 are brazed to the front and rear side surfaces, respectively, of the outside plate 7 and the intermediate plate 9. The projecting end of each of the cover walls 19 has a plurality of integrally formed engaging portions 21 which are vertically spaced apart from one another. The engaging portions 21 of the cover walls 19 are engaged with and brazed to the outer surface of the outside plate 7. The inside plate 8 is formed, by press work, from an aluminum brazing sheet having a brazing material layer on each of opposite sides.

The intermediate plate 9 has communication holes 22 in the form of through-holes for allowing the tube insertion holes 18 of the inside plate 8 to communicate with the interiors of the outwardly bulging portions 11A and 11B and in a number equal to the number of the tube insertion holes 18. The communication holes 22 positionally coincide with the respective tube insertion holes 18 of the inside plate 8 and have the same width as the tube insertion holes 18. The intermediate plate 9 has stepped portions 25 formed on the peripheral wall surface of each communication hole 22 of the intermediate plate 9 at opposite end portions thereof with respect to the hole-length direction (front and rear end portions) such that the stepped portions 25 are located at an intermediate position with respect to the thickness direction of the intermediate plate 9. The stepped portions 25 project inward with respect to the hole-length direction of the communication hole 22. A corresponding end surface of the corresponding heat exchange tube 4 engages the stepped portions 25. The projecting height of the stepped portion 25 of the intermediate plate 9 from the peripheral wall surface of the communication hole 22 is determined so as not to cover refrigerant channels 4 a, which will be described later, of the heat exchange tube 4. An upper-half group of tube insertion holes 18 of the inside plate 8 communicate with the interior of the upper outwardly bulging portion 11A via an upper-half group of respective communication holes 22 of the intermediate plate 9. Similarly, a lower-half group of tube insertion holes 18 communicate with the interior of the lower outwardly bulging portion 11B via a lower-half group of respective communication holes 22 of the intermediate plate 9. All of the communication holes 22 in communication with the interior of the upper outwardly bulging portion 11A communicate with one another via communication portions 23, and all of the communication holes 22 in communication with the interior of the lower outwardly bulging portion 11B communicate with one another via other communication portions 23. The communication portions 23 are formed by cutting off portions between the adjacent communication holes 22 in the intermediate plate 9. Thus, the intermediate plate 9 has a refrigerant flow section communicating with the refrigerant flow section within the outwardly bulging portion 11A, and a refrigerant flow section communicating with the refrigerant flow section within the outwardly bulging portion 11B.

The second header tank 3 has substantially the same construction as the first header tank 2, and like features and parts are designated by like reference numerals. The two header tanks 2 and 3 are disposed such that the respective inside plates 8 face each other. The second header tank 3 differs from the first header tank 2 in that the outside plate 7 has dome-like outwardly bulging portions provided in a number one fewer than the outwardly bulging portions 11A and 11B of the first header tank 2; herein, a single dome-like outwardly bulging portion 24, which extends from an upper end portion to a lower end portion of the outside plate 7 and is opposed to the outwardly bulging portions 11A and 11B of the first header tank 2; the outwardly bulging portion 24 does not have a refrigerant inlet and a refrigerant outlet; all of the tube insertion holes 18 of the inside plate 8 communicate with the interior of the outwardly bulging portion 24 via all of the respective communication holes 22 of the intermediate plate 9; and all of the communication holes 22 of the intermediate plate 9 communicate with one another via the communication portions 23, which are formed by cutting off portions between the adjacent communication holes 22. The outwardly bulging portion 24 has the same bulging height and width as the outwardly bulging portions 11A and 11B of the first header tank 2. In the outside plate 7, a peripheral portion around a rightward-facing opening of the outwardly bulging portion 24 is brazed to the intermediate plate 9, whereby the intermediate plate 9 covers the rightward-facing opening of the outwardly bulging portion 24. As a result, the interior of the outwardly bulging portion 24 serves as a refrigerant flow section whose upper and lower ends are closed. A portion of the second header tank 3 which corresponds to the outwardly bulging portion 24 serves as a header section. The thickness of the outside plate 7 is 2 mm or greater. All of the communication holes 22 and the communication portions 23 of the intermediate plate 9 form a refrigerant flow section communicating with the refrigerant flow section within the outwardly bulging portion 24. In the second header tank 3 as well, the curvature radius R of a connection portion 26 between the inner wall surface of the outwardly bulging portion 24 and each of inside surfaces of the outside plate 7 which are located on the front and rear sides of the outwardly bulging portion 24 and which extend in the left-right direction is not greater than 1 mm, preferably, not greater than 0.5 mm.

The two header tanks 2 and 3 are manufactured as shown in FIGS. 7 to 9.

First, an outside-plate forming metal plate 60, which is composed of an aluminum brazing sheet having a brazing material layer on each of opposite sides, is subjected to a press work so as to form the outside plates 7 each having the outwardly bulging portions 11A and 11B or the outwardly bulging portion 24 as shown in FIG. 7. That is, a first press work is performed on the outside-plate forming metal plate 60 as shown FIG. 7(a) by making use of a first upper die 61 having a thick-portion forming recess 62 on the lower surface thereof, and a first lower die 63 having a pair of side-edge restraining projections 64 on the upper surface thereof, whereby a thick portion 65 is formed at a central portion with respect to the width direction, the thick portion having a thickness grater than that of thin portions on the opposite sides of the thick portion (see FIG. 7(b)). Preferably, the thickness of the thick portion 65 is 1.05 to 1.5 times the thickness of the thin portions. When the thickness of the thick portion 65 is less than 1.05 times the thickness of the thin portions, it become difficult to form the connection portion 26 to have a curvature radius R of 1 mm or less in a second press work, which will be described later. Further, it is difficult to from the thick portion 65 by press work to have a thickness greater than 1.5 times the thickness of the thin portions. In the illustrated example, the thick portion 65 is formed by the first press work in such a manner that a central portion of the outside-plate forming metal plate 60 with respect to the width direction swell upward. However, the method of forming the thick portion 65 is not limited thereto, and the thick portion 65 may be formed by swelling the central portion of the outside-plate forming metal plate 60 downward or swelling the central portion of the outside-plate forming metal plate 60 upward and downward.

Subsequently, a second press work is performed on the outside-plate forming metal plate 60 having the thick portion 65 by making use of a second upper die 66 and a second lower die 68. The second upper die 66 has, on the lower surface, a concave portion 67 for forming the outer shape of an outwardly bulging portion 11A (11B, 24). The second lower die 68 has, on the upper surface, a convex portion 69 for forming the inner shape of the outwardly bulging portion 11A (11B, 24), and a pair of side-edge restraining projections 70. Thus, the outwardly bulging portion 11A (11B, 24) is formed by making use of the thick portion 65 (see FIG. 7(c)). At this time, the aluminum material of the outside-plate forming metal plate 60 flows throughout the space formed between the concave portion 67 of the second upper die 66 and the convex portion 69 of the second lower die 68. Thus, the curvature radius R of the connection portion 26 between the inner wall surface of the outwardly bulging portion 11A (11B, 24) and the lower surfaces of the outside plate 7 located on the front and rear sides of the outwardly bulging portion 11A (11B, 24) and being continuous with the inner wall surface can be made 1 mm or smaller. In this manner, the outside plate 7 is manufactured. Notably, the refrigerant inlet 12 and the refrigerant outlet 15 are formed in the outside plate 7 for the first header tank 2.

Also, an aluminum brazing sheet having a brazing material layer on each of opposite sides is subjected to a press work so as to form the inside plates 8 each having the tube insertion holes 18, the cover walls 19, and engaging-portion-forming lugs 21A extending straight from the cover walls 19. Furthermore, a bare aluminum material is subjected to a press work so as to form the intermediate plates 9 each having the communication holes 22, the stepped portions 25, and the communication portions 23.

Next, as shown in FIGS. 8 and 9, the three plates 7, 8, and 9 are stacked, and the lugs 21A are bent so as to form the engaging portions 21 engaged with the outside plate 7, thereby forming a provisional assembly. Subsequently, the provisional assemblies are heated at a predetermined temperature, whereby, by use of the brazing material layers of the outside plate 7 and the brazing material layers of the inside plate 8, the three plates 7, 8, and 9 are brazed together, the cover walls 19 and the front and rear end surfaces of the intermediate plate 9 and the outside plate 7 are brazed together, and the engaging portions 21 and the outside plate 7 are brazed together. Thus are manufactured the two header tanks 2 and 3.

As shown in FIGS. 10 and 11, the heat exchange tube 4 includes mutually opposed flat upper and lower walls 31 and 32 (a pair of flat walls); front and rear side walls 33 and 34 which extend between front and rear side ends, respectively, of the upper and lower walls 31 and 32; and a plurality of reinforcement walls 35 which are provided at predetermined intervals between the front and rear side walls 33 and 34 and extend longitudinally and between the upper and lower walls 31 and 32. By virtue of this structure, the heat exchange tube 4 internally has a plurality of refrigerant channels 4 a arranged in the width direction thereof.

The front side wall 33 has a double-wall structure and includes an outer side-wall-forming elongated projection 36 which is integrally formed with the front side end of the upper wall 31 in a downward raised condition and extends along the entire height of the heat exchange tube 4; an inner side-wall-forming elongated projection 37 which is located inside the outer side-wall-forming elongated projection 36 and is integrally formed with the upper wall 31 in a downward raised condition; and an inner side-wall-forming elongated projection 38 which is integrally formed with the front side end of the lower wall 32 in an upward raised condition. The outer side-wall-forming elongated projection 36 is brazed to the two inner side-wall-forming elongated projections 37 and 38 and the lower wall 32 while a lower end portion thereof is engaged with a front side edge portion of the lower surface of the lower wall 32. The two inner side-wall-forming elongated projections 37 and 38 are brazed together while butting against each other. The rear side wall 34 is integrally formed with the upper and lower walls 31 and 32. A projection 38 a is integrally formed on the tip end face of the inner side-wall-forming projection 38 of the lower wall 32 and extends in the longitudinal direction of the inner side-wall-forming projection 38 along the entire length thereof. A groove 37 a is formed on the tip end face of the inner side-wall-forming elongated projection 37 of the upper wall 31 and extends in the longitudinal direction of the inner side-wall-forming elongated projection 37 along the entire length thereof. The projection 38 a is press-fitted into the groove 37 a.

The reinforcement walls 35 are formed such that reinforcement-wall-forming elongated projections 40 and 41, which are integrally formed with the upper wall 31 in a downward raised condition, and reinforcement-wall-forming elongated projections 42 and 43, which are integrally formed with the lower wall 32 in an upward raised condition, are brazed together while the reinforcement-wall-forming elongate projections 40 and 41 butt against the reinforcement-wall-forming elongated projections 43 and 42, respectively. The upper wall 31 has the reinforcement-wall-forming elongated projections 40 and 41, which are of different projecting heights and are arranged alternately in the front-rear direction. The lower wall 32 has the reinforcement-wall-forming elongated projections 42 and 43, which are of different projecting heights and are arranged alternately in the front-rear direction. The reinforcement-wall-forming elongated projections 40 of a long projecting height of the upper wall 31 and the respective reinforcement-wall-forming elongated projections 43 of a short projecting height of the lower wall 32 are brazed together. The reinforcement-wall-forming elongated projections 41 of a short projecting height of the upper wall 31 and the respective reinforcement-wall-forming elongated projections 42 of a long projecting height of the lower wall 32 are brazed together. Hereinafter, the reinforcement-wall-forming elongated projections 40 and 42 of a long projecting height of the upper and lower walls 31 and 32 are called the first reinforcement-wall-forming elongated projections. Similarly, the reinforcement-wall-forming elongated projections 41 and 43 of a short projecting height of the upper and lower walls 31 and 32 are called the second reinforcement-wall-forming elongated projections. A groove 44 (45) is formed on the tip end face of the second reinforcement-wall-forming elongated projection 41 (43) of the upper wall 31 (lower wall 32) and extends in the longitudinal direction of the second reinforcement-wall-forming elongated projection 41 (43) along the entire length thereof. A tip end portion of the first reinforcement-wall-forming elongated projection 42 (40) of the lower wall 32 (upper wall 31) is fitted into the groove 44 (45) of the second reinforcement-wall-forming elongated projection 41 (43) of the upper wall 31 (lower wall 32). While tip end portions of the first reinforcement-wall-forming elongated projections 40 and 42 of the upper and lower walls 31 and 32, respectively, are fitted into the respective grooves 45 and 44, the reinforcement-wall-forming elongated projections 40 and 43 are brazed together, and the reinforcement-wall-forming elongated projections 41 and 42 are brazed together.

The heat exchange tube 4 is manufactured by use of a tube-forming metal sheet 50 as shown in FIG. 12(a). The tube-forming metal sheet 50 is formed, by rolling, from an aluminum brazing sheet having a brazing material layer on each of opposite sides. The tube-forming metal sheet 50 includes a flat upper-wall-forming portion 51 (flat-wall-forming portion); a flat lower-wall-forming portion 52 (flat-wall-forming portion); a connection portion 53 connecting the upper-wall-forming portion 51 and the lower-wall-forming portion 52 and adapted to form the rear side wall 34; the inner side-wall-forming elongated projections 37 and 38, which are integrally formed with the side ends of the upper-wall-forming and lower-wall-forming portions 51 and 52 opposite the connection portion 53 in an upward raised condition and which are adapted to form an inner portion of the front side wall 33; an outer side-wall-forming-elongated-projection forming portion 54, which extends outward from the side end of the upper-wall-forming portion 51 opposite the connection portion 53; and a plurality of reinforcement-wall-forming elongated projections 40, 41, 42, and 43, which are integrally formed with the upper-wall-forming and lower-wall-forming portions 51 and 52 in an upward raised condition and which are arranged at predetermined intervals in the width direction of the tube-forming metal sheet 50. The first reinforcement-wall-forming elongated projections 40 of the upper-wall-forming portion 51 and the second reinforcement-wall-forming elongated projections 43 of the lower-wall-forming portion 52 are located symmetrically with respect to the centerline of the width direction of the connection portion 53. Similarly, the second reinforcement-wall-forming elongated projections 41 of the upper-wall-forming portion 51 and the first reinforcement-wall-forming elongated projections 42 of the lower-wall-forming portion 52 are located symmetrically with respect to the centerline of the width direction of the connection portion 53. The projection 38 a is formed on the tip end face of the inner side-wall-forming elongated projection 38 of the lower-wall-forming portion 52, and the groove 37 a is formed on the tip end face of the inner side-wall-forming elongated projection 37 of the upper-wall-forming portion 51. The groove 44 (45), into which a tip end portion of the first reinforcement-wall-forming elongated projection 42 (40) of the lower-wall-forming portion 52 (upper-wall-forming portion 51) is fitted, is formed on the tip end face of the second reinforcement-wall-forming elongated projection 41 (43) of the upper-wall-forming portion 51 (lower-wall-forming portion 52).

The inner side-wall-forming elongated projections 37 and 38 and the reinforcement-wall-forming elongated projections 40, 41, 42, and 43 are integrally formed, by rolling, on one side of the aluminum brazing sheet whose opposite sides are clad with a brazing material, whereby a brazing material layer (not shown) is formed on the opposite side surfaces and tip end faces of the inner side-wall-forming elongated projections 37 and 38 and the reinforcement-wall-forming elongated projections 40, 41, 42, and 43; on the peripheral surfaces of the grooves 44 and 45 of the second reinforcement-wall-forming elongated projections 41 and 43; and on the vertically opposite surfaces of the upper-wall-forming and lower-wall-forming portions 51 and 52 and the outer side-wall-forming-elongated-projection forming portion 54.

The tube-forming metal sheet 50 is gradually folded at opposite side edges of the connection portion 53 by a roll forming process (see FIG. 12(b)) until a hairpin form is assumed. The inner side-wall-forming elongated projections 37 and 38 are caused to butt against each other; tip end portions of the first reinforcement-wall-forming elongated projections 40 and 42 are fitted into the respective grooves 45 and 44 of the second reinforcement-wall-forming elongated projections 43 and 41; and the projection 38 a is press-fitted into the groove 37 a.

Next, the outer side-wall-forming-elongated-projection forming portion 54 is folded along the outer surfaces of the inner side-wall-forming elongated projections 37 and 38, and a tip end portion thereof is deformed so as to be engaged with the lower-wall-forming portion 52, thereby yielding a folded member 55 (see FIG. 12(c)).

Subsequently, the folded member 55 is heated at a predetermined temperature so as to braze together tip end portions of the inner side-wall-forming elongated projections 37 and 38; to braze together tip end portions of the first and second reinforcement-wall-forming elongated projections 40 and 43; to braze together tip end portions of the first and second reinforcement-wall-forming elongated projections 42 and 41; and to braze the outer side-wall-forming-elongated-projection forming portion 54 to the inner side-wall-forming elongated projections 37 and 38 and to the lower-wall-forming portion 52. Thus is manufactured the heat exchange tube 4.

While opposite end portions of the heat exchange tubes 4 are inserted through the respective tube insertion holes 18 of the inside plates 8 and into the respective communication holes 22 of the intermediate plates 9 of the header tanks 2 and 3, and end surfaces of the opposite end portions abut the respective stepped portions 25 of the intermediate plates 9, the opposite end portions of the heat exchange tubes 4 are brazed to the respective peripheral wall surfaces of the tube insertion holes 18 of the inside plates 8 and to the respective peripheral wall surfaces of the communication holes 22 of the intermediate plates 9 by utilization of the brazing material layers of the inside plates 8 and the brazing material layers of the tube-forming metal sheets 50.

Accordingly, right end portions of an upper-half group of heat exchange tubes 4 are connected to the first header tank 2 so as to communicate with the interior of the upper outwardly bulging portion 11A, and left end portions are connected to the second header tank 3 so as to communicate with the interior of the outwardly bulging portion 24. Also, right end portions of a lower-half group of heat exchange tubes 4 are connected to the first header tank 2 so as to communicate with the interior of the lower outwardly bulging portion 11B, and left end portions are connected to the second header tank 3 so as to communicate with the interior of the outwardly bulging portion 24.

Each of the corrugated fins 5 is made in a wavy form from a brazing sheet; herein, an aluminum brazing sheet, having a brazing material layer on each of opposite sides.

The gas cooler 1 is manufactured by the steps of: preparing the aforementioned two provisional assemblies to be manufactured into the header tanks 2 and 3, a plurality of the aforementioned folded members 55, and a plurality of corrugated fins 5; arranging the two provisional assemblies in such a manner as to be spaced apart from each other with the inside plates 8 facing each other; arranging alternately the folded members 55 and the corrugated fins 5; inserting opposite end portions of the folded members 55 through the respective tube insertion holes 18 of the inside plates 8 and into the respective communication holes 22 of the intermediate plates 9 of the two provisional assemblies, and causing the end surfaces of the opposite end portions to abut the respective stepped portions 25 of the intermediate plate 9; arranging the side plates 6 externally of the respective opposite-end corrugated fins 5; arranging the inlet member 13 and the outlet member 16 on the outwardly bulging portions 11A and 11B, respectively, of the outside plate 7 used to form the first header tank 2; and brazing necessary portions of the provisional assemblies as mentioned above to thereby form the header tanks 2 and 3, brazing necessary portions of the folded members 55 as mentioned above to thereby form the heat exchange tubes 4, brazing the heat exchange tubes 4 to the header tanks 2 and 3, brazing the corrugated fins 5 to the heat exchange tubes 4, brazing the side plates 6 to the respective corrugated fins 5, and brazing the inlet member 13 and the outlet member 16 to the outwardly bulging portions 11A and 11B, respectively.

The gas cooler 1, together with a compressor, an evaporator, a pressure-reducing device, and an intermediate heat exchanger for performing heat exchange between refrigerant from the gas cooler and refrigerant from the evaporator, constitutes a supercritical refrigeration cycle. The refrigeration cycle is installed in a vehicle, for example, in an automobile, as a car air conditioner.

In the gas cooler 1 described above, CO₂ from a compressor flows through the refrigerant inflow channel 14 of the inlet member 13 and enters the upper outwardly bulging portion 11A of the first header tank 2 through the refrigerant inlet 12. Then, the CO₂ dividedly flows into the refrigerant channels 4 a of all the heat exchange tubes 4 in communication with the upper outwardly bulging portion 11A. The CO₂ in the refrigerant channels 4 a flows leftward through the refrigerant channels 4 a and enters the outwardly bulging portion 24 of the second header tank 3. The CO₂ in the outwardly bulging portion 24 flows downward through the interior of the outwardly bulging portion 24 and through the communication portions 33 of the intermediate plate 9; dividedly flows into the refrigerant channels 4 a of all the heat exchange tubes 4 in communication with the lower outwardly bulging portion 11B; changes its course; flows rightward through the refrigerant channels 4 a; and enters the lower outwardly bulging portion 11B of the first header tank 2. Subsequently, the CO₂ flows out of the gas cooler 1 via the refrigerant outlet 15 and the refrigerant outflow channel 17 of the outlet member 16. While flowing through the refrigerant channels 4 a of the heat exchange tubes 4, the CO₂ is subjected to heat exchange with the air flowing through the air-passing clearances in the direction of arrow X shown in FIG. 1, thereby being cooled.

FIG. 13 shows another method of manufacturing the outside plates 7 of the two header tanks 2 and 3.

First, a first press work is performed on an outside-plate forming metal plate 60, which is composed of an aluminum brazing sheet having a brazing material layer on each of opposite sides as shown in FIG. 13(a), by use of a first upper die 80 and a first lower die 82. The first upper die 80 has, on the lower surface, a concave portion 81 having a depth greater than the height of the outwardly bulging portion 11A (11B, 24) as measured on the outer side thereof. The first lower die 82 has, on the upper surface, a convex portion 83 having a height greater than the height of the outwardly bulging portion 11A (11B, 24) as measured on the inner side thereof. Thus, a preliminary bulging portion 84 having a bulging height greater than the outwardly bulging portion 11A (11B, 24) is formed (see FIG. 13(b)).

Subsequently, a second press work is performed on the outside-plate forming metal plate 60 by making use of a second upper die 85 and a second lower die 89. The second upper die 85 has, on the lower surface, a concave portion 86 for forming the outer shape of the outwardly bulging portion 11A (11B, 24), and a pair of projections 88 having cutting blades 87 at their lower ends and restraining the outside-plate forming metal plate 60 from opposite sides with respect to the width direction. The second lower die 89 has, on the upper surface, a convex portion 90 for forming the inner shape of the outwardly bulging portion 11A (11B, 24). Before the preliminary bulging portion 84 is formed into the outwardly bulging portion 11A (11B, 24), opposite side edge portions of the outside-plate forming metal plate 60 are cut by means of the cutting blades 87 of the projections 88 of the second upper die 85. After this cutting, the preliminary bulging portion 84 is formed into outwardly bulging portion 11A (11B, 24) by the concave portion 86 and the convex portion 90, while the outside-plate forming metal plate 60 having the preliminary bulging portion 84 is restricted from opposite sides with respect to the width direction by the projections 88 of the second upper die 85 (see FIG. 13(c)). At this time, the aluminum material of the outside-plate forming metal plate 60 flows throughout the space formed between the concave portion 86 of the second upper die 85 and the convex portion 90 of the second lower die 89. Thus, the curvature radius R of the connection portion 26 between the inner wall surface of the outwardly bulging portion 11A (11B, 24) and the lower surfaces of the outside plate 7 located on the front and rear sides of the outwardly bulging portion 11A (11B, 24) and being continuous with the inner wall surface can be made 1 mm or smaller. In this manner, the outside plate 7 is manufactured.

In the above-described embodiment, each outside plate 7 is formed of an aluminum brazing sheet having a brazing material layer on each of opposite sides, and the outside plate 7 and the intermediate plate 9 are brazed together by making use of the brazing material layer of the outside plate 7. However, the manner of brazing the outside plate 7 and the intermediate plate 9 is not limited thereto, and the outside plate 7 and the intermediate plate 9 may be brazed as follows. Each outside plate 7 is formed of an aluminum brazing sheet having a brazing material layer only on an outer surface in the left-right direction (a surface facing opposite to the corresponding intermediate plate 9); the intermediate plate 9 is formed of an aluminum brazing sheet having a brazing material layer only on an outer surface in the left-right direction (a surface facing the outside plate 7); and the outside plate 7 and the intermediate plate 9 are brazed together by making use of the brazing material layer of the intermediate plate 9.

In the above-described embodiment, the heat exchanger of the present invention is applied to a gas cooler of a supercritical refrigeration cycle. However, the heat exchanger of the present invention may be applied to an evaporator of the above-mentioned supercritical refrigeration cycle. This evaporator, together with a compressor, a gas cooler, a pressure-reducing device, and an intermediate heat exchanger for performing heat exchange between refrigerant from the gas cooler and refrigerant from the evaporator, constitutes a supercritical refrigeration cycle which uses a supercritical refrigerant such as CO₂. This refrigeration cycle is installed in a vehicle, for example, in an automobile, as a car air conditioner. Moreover, the method of manufacturing outside plates according to the present invention can be applied to manufacture of the outside plates of the header tanks of the evaporator of the above-mentioned supercritical refrigeration cycle.

Although CO₂ is used as a supercritical refrigerant of a supercritical refrigeration cycle in the above-described embodiments, the refrigerant is not limited thereto, but ethylene, ethane, nitrogen oxide, or the like may be alternatively used.

The above-described embodiment uses, for forming the heat exchange tube 4, a folded member 55 which is formed by bending a tube-forming metal sheet in the form of an aluminum brazing sheet having a brazing material layer on each of opposite sides. However, the present invention is not limited thereto. For example, an aluminum extrudate having a brazing material layer on its outer surface may be used to form the heat exchange tube 4. 

1. A heat exchanger comprising a pair of header tanks disposed apart from each other and a plurality of flat heat exchange tubes disposed in parallel between the two header tanks and having opposite end portions connected to the respective header tanks, each of the two header tanks being configured such that an outside plate, an inside plate, and an intermediate plate intervening between the outside and inside plates are brazed together in layers, the outside plate having an outwardly bulging portion extending in a longitudinal direction thereof and having an opening closed by the intermediate plate, the inside plate having a plurality of tube insertion holes in the form of through-holes formed in a region corresponding to the outwardly bulging portion of the outside plate and spaced apart from one another along a longitudinal direction of the inside plate, and the intermediate plate having a plurality of communication holes in the form of through-holes formed for allowing the respective tube insertion holes of the inside plate to communicate with the interior of the outwardly bulging portion of the outside plate, wherein the outside plate of each header tank is formed of a metal plate and through a press work performed thereon, and a connection portion between an inner wall surface of the outwardly bulging portion of the outside plate and a surface of the outside plate which surface is joined to the intermediate plate has a curvature radius of 1 mm or less.
 2. A heat exchanger according to claim 1, wherein the connection portion between the inner wall surface of the outwardly bulging portion and the surface of the outside plate joined to the intermediate plate has a curvature radius of 0.5 mm or less.
 3. A heat exchanger according to claim 1, wherein the outside plate has a thickness of 2 mm or greater.
 4. A method of manufacturing an outside plate used for a heat exchanger header tank which is configured such that an outside plate, an inside plate, and an intermediate plate intervening between the outside and inside plates are brazed together in layers, the outside plate having an outwardly bulging portion extending in a longitudinal direction thereof and having an opening closed by the intermediate plate, the inside plate having a plurality of tube insertion holes in the form of through-holes formed in a region corresponding to the outwardly bulging portion of the outside plate and spaced apart from one another along a longitudinal direction of the inside plate, and the intermediate plate having a plurality of communication holes in the form of through-holes formed for allowing the respective tube insertion holes of the inside plate to communicate with the interior of the outwardly bulging portion of the outside plate, the method comprising the steps of: forming a thick portion on an outside-plate forming metal plate at a center portion with respect to the width direction thereof, the thick portion being thicker than the remaining thin portion; and performing a press work on the outside-plate forming metal plate so as to form the outwardly bulging portion by making use of the thick portion such that a connection portion having a curvature radius of 1 mm or less is formed between an inner wall surface of the outwardly bulging portion and each of surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface.
 5. A method of manufacturing an outside plate used for a heat exchanger header tank according to claim 4, wherein the thick portion is formed by performing a press work on the outside-plate forming metal plate.
 6. A method of manufacturing an outside plate used for a heat exchanger header tank according to claim 5, wherein the thick portion of the outside-plate forming metal plate has a thickness 1.05 to 1.5 times that of the remaining thin portion.
 7. A method of manufacturing an outside plate used for a heat exchanger header tank according to claim 4, wherein a connection portion having a curvature radius of 0.5 mm or less is formed between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface.
 8. A method of manufacturing an outside plate used for a heat exchanger header tank according to claim 4, wherein the outside plate has a thickness of 2 mm or greater in its final shape.
 9. A method of manufacturing an outside plate used for a heat exchanger header tank which is configured such that an outside plate, an inside plate, and an intermediate plate intervening between the outside and inside plates are brazed together in layers, the outside plate having an outwardly bulging portion extending in a longitudinal direction thereof and having an opening closed by the intermediate plate, the inside plate having a plurality of tube insertion holes in the form of through-holes formed in a region corresponding to the outwardly bulging portion of the outside plate and spaced apart from one another along a longitudinal direction of the inside plate, and the intermediate plate having a plurality of communication holes in the form of through-holes formed for allowing the respective tube insertion holes of the inside plate to communicate with the interior of the outwardly bulging portion of the outside plate, the method comprising the steps of: performing a first press work on an outside-plate forming metal plate so as to form a preliminary bulging portion having a bulging height greater than that of the outwardly bulging portion; and performing a second press work on the outside-plate forming metal plate having the preliminary bulging portion, while restraining the outside-plate forming metal plate from the opposite sides with respect to the width direction thereof, so as to form the outwardly bulging portion from the preliminary bulging portion such that a connection portion having a curvature radius of 1 mm or less is formed between an inner wall surface of the outwardly bulging portion and each of surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface.
 10. A method of manufacturing an outside plate used for a heat exchanger header tank according to claim 9, wherein the step of performing the second press work includes cutting opposite side edge portions of the outside-plate forming metal plate by use of one of dies used for the press work before formation of the outwardly bulging portion from the preliminary bulging portion, and restraining the outside-plate forming metal plate having the preliminary bulging portion from the opposite sides with respect to the width direction thereof by use of the die.
 11. A method of manufacturing an outside plate used for a heat exchanger header tank according to claim 9, wherein a connection portion having a curvature radius of 0.5 mm or less is formed between the inner wall surface of the outwardly bulging portion and each of the surfaces of the outside plate located on the opposite sides of the outwardly bulging portion and being continuous with the inner wall surface.
 12. A method of manufacturing an outside plate used for a heat exchanger header tank according to claim 9, wherein the outside plate has a thickness of 2 mm or greater in its final shape. 